Specific manipulation in vivo of immunity to skin grafts bearing multiple minor histocompatibility differences

Cell Therapy as a Tool for Induction of Immunological Tolerance after Liver Transplantation

Transplantation of solid organs, including liver, induces a number of serious complications related to immune incompatibility and requiring long-term use of immunosuppressive drugs. Finding the ways to inducing recipient immunological tolerance to the grafts is a top priority in organ transplantation and immunology. Along with the search for immunosupressive therapy, the development of alternative approaches to induction of immunological tolerance based on cell technologies is now in progress. In this regard, studies of the so-called spontaneous operational tolerance observed in ~20% patients after orthotopic liver transplantation is a promising trend. Understanding of this phenomenon can shed light on the mechanisms of immunological tolerance to allografts and will help to identify specific tolerance biomarkers and cell types with the aptitude for the induction of tolerance to liver allografts.

Liver immunology: How to reconcile tolerance with autoimmunity

There are several examples of liver tolerance: the relative ease by which liver allografts are accepted and the exploitation of the hepatic microenvironment by the malarial parasite and hepatotrophic viruses are notable examples. The vasculature of the liver supports a unique population of antigen presenting cells specialised to maintain immunological tolerance despite continuous exposure to gut-derived antigens. Liver sinusoidal endothelial cells and Kupffer cells appear to be key to the maintenance of immune tolerance, by promoting T cell anergy or deletion and the generation of regulatory cell subsets. Despite this, there are three liver diseases with likely autoimmune involvement: primary biliary cirrhosis, primary sclerosing cholangitis and autoimmune hepatitis. How can we reconcile this with the inherent tolerogenicity of the liver? Genetic studies have uncovered several associations with genes involved in the activation of the innate and adaptive immune systems. There is also evidence pointing to pathogenic and xenobiotic triggers of autoimmune liver disease. Coupled to this, impaired immunoregulatory mechanisms potentially play a permissive role, allowing the autoimmune response to proceed.

Pretransplant infusion of mesenchymal stem cells prolongs the survival of a semiallogeneic heart transplant through the generation of regulatory T cells

In this study, we investigated whether mesenchymal stem cells (MSC) had immunomodulatory properties in solid organ allotransplantation, using a semiallogeneic heart transplant mouse model, and studied the mechanism(s) underlying MSC tolerogenic effects. Either single (portal vein, day -7) or double (portal vein, day -7 and tail vein, day -1) pretransplant infusions of donor-derived B6C3 MSC in B6 recipients induced a profound T cell hyporesponsiveness and prolonged B6C3 cardiac allograft survival. The protolerogenic effect was abrogated when donor-derived MSC were injected together with B6C3 hematopoietic stem cells (HSC), suggesting that HSC negatively impact MSC immunomodulatory properties. Both the induction (pretransplant) and the maintenance phase (>100 days posttransplant) of donor-derived MSC-induced tolerance were associated with CD4(+)CD25(+)Foxp3(+) Treg expansion and impaired anti-donor Th1 activity. MSC-induced regulatory T cells (Treg) were donor-specific since adoptive transfer of splenocytes from tolerant mice prevented the rejection of fully MHC-mismatched donor-specific secondary allografts but not of third-party grafts. In addition, infusion of recipient-derived B6 MSC tolerized a semiallogeneic B6C3 cardiac allograft, but not a fully MHC-mismatched BALB/c graft, and expanded Treg. A double i.v. pretransplant infusion of recipient-derived MSC had the same tolerogenic effect as the combined intraportal/i.v. MSC infusions, which makes the tolerogenic protocol applicable in a clinical setting. In contrast, single MSC infusions given either peritransplant or 1 day after transplant were less effective. Altogether these findings indicate that MSC immunomodulatory properties require HSC removal, partial sharing of MHC Ags between the donor and the recipient and pretransplant infusion, and are associated with expansion of donor-specific Treg.

Cellular and molecular mechanisms of liver tolerance

The liver exhibits a distinctive form of immune privilege, termed liver tolerance, in which orthotopic liver transplantation results in systemic donor-specific T-cell tolerance, while antigens introduced either into hepatocytes or via the portal vein also cause tolerance. Here we argue that the fundamental mechanism driving liver tolerance is likely to be the continuous exposure of diverse liver cell types to endotoxin, derived from the intestinal bacteria. This exposure promotes the expression of a set of cytokines, antigen-presenting molecules, and costimulatory signals that impose T-cell inactivation, partly via effects on liver antigen-presenting cells. The evidence favors clonal deletion mechanisms and is consistent with a role for regulatory T cells but does not support either anergy or immune deviation as important factors in liver tolerance.

Targeted bone marrow radioablation with 153Samarium-lexidronam promotes allogeneic hematopoietic chimerism and donor-specific immunologic hyporesponsiveness

BACKGROUND

Transplantation tolerance, defined as acceptance of a graft by an otherwise fully immunocompetent host, has been an elusive goal. Although robust tolerance has been achieved by the induction of stable hematopoietic chimerism after bone marrow transplantation, lethal or sublethal radiation conditioning used to induce long-term chimerism precludes its clinical use. We studied whether targeted delivery of radiation to bone marrow could allow for bone marrow cell (BMC) engraftment, chimerism, and donor-specific tolerance in the absence of the side effects associated with external irradiation.

METHODS

We administered a radioactive bone-seeking compound (Samarium-Lexidronam, Quadramet, Berlex Laboratories, Wayne, NJ) together with transient T-cell costimulatory blockade to recipient mice. Allogeneic BMCs were given 7 or 14 days after preconditioning. Costimulatory blockade was obtained by the use of an anti-CD154 antibody for 4 weeks. Chimerism was assessed by flow cytometry. Mice then received donor-specific and third-party skin grafts. Graft survival was analyzed with mechanisms of donor-specific hyporesponsiveness.

RESULTS

High levels of stable chimerism across an allogeneic barrier were achieved in mice by a single administration of Samarium-Lexidronam, transient T-cell costimulatory blockade, and BMC transplantation. A large percentage of chimeric animals retained donor-derived skin grafts for more than 120 days without requiring additional immunosuppression, suggesting that harsh cytotoxic preconditioning is not necessary to achieve stable chimerism and donor specific hyporesponsiveness. Analysis of the T-cell repertoire in chimeras indicates T-cell deletional mechanisms.

CONCLUSIONS

These data broaden the potential use of BMC transplantation for tolerance induction and argue for its potential in treating autoimmune diseases.

Evidence of a role for CD200 in regulation of immune rejection of leukaemic tumour cells in C57BL/6 mice

Increased expression of the molecule CD200 in mice receiving renal allografts is associated with immunosuppression leading to increased graft survival, and altered cytokine production in lymphocytes harvested from the transplanted animals. Preferential production of IL-4, IL-10 and TGFbeta occurs on donor-specific restimulation in vitro, with decreased production of IL-2, IFNgamma and TNFalpha. These effects are enhanced by simultaneous infusion of CD200 immunoadhesin (CD200Fc) and donor CD200 receptor (CD200r) bearing macrophages to transplanted mice. C57BL/6 mice do not normally resist growth of EL4 or C1498 leukaemia tumour cells. Following transplantation of cyclophosphamide-treated C57BL/6 with T-depleted C3H bone marrow cells, or for the EL4 tumour, immunization of C57BL/6 mice with tumour cells transfected with a vector encoding the co-stimulatory molecule CD80 (EL4-CD80), mice resist growth of tumour challenge. Immunization of C57BL/6 mice with EL4 cells overexpressing CD86 (EL4-CD86) is ineffective. Protection from tumour growth in either model is suppressed by infusion of CD200Fc, an effect enhanced by co-infusion of CD200r+ macrophages. CD200Fc acts on both CD4+ and CD8+ cells to produce this suppression. These data are consistent with the hypothesis that immunosuppression following CD200-CD200r interaction can regulate a functionally important tumour growth inhibition response in mice.

Preparation and functional properties of polyclonal and monoclonal antibodies to murine MD-1

Rabbits, rats and hamsters were immunized with KLH-coupled synthetic peptide sequences of the murine MD-1 molecule. Serum from immunized animals bound in Western gels to a 25 KDa protein extracted from LPS stimulated mouse spleen cells, as did a rat hybridoma (SH1.2.47) prepared from peptide-immunized rats. CHO cells transfected with a plasmid cDNA construct encoding murine MD-1, the target antigen for the antibodies in question, were also stained (in FACS) by the same antibodies. Patching and capping of the antigen(s) detected by any one of these sera abolished binding of all antibodies in subsequent FACS analysis, consistent with the hypothesis that they all detected the same antigen. In a final study to assess the possible involvement of MD-1 in regulation of cell activation for cytokine production following allostimulation, we found that all of the antibodies inhibited IL-2 and IFNgamma production, while enhancing IL-4 and IL-10 production, in mixed leukocyte reactions (MLR) in vitro.

Successful allogeneic bone marrow transplantation (BMT) by injection of bone marrow cells via portal vein: stromal cells as BMT-facilitating cells

We examined the importance of the coadministration of bone marrow (BM) stromal cells with BM cells via the portal vein. A significant increase in the number of day-14 colony-forming unit-spleen (CFU-S) was observed in the recipient mice injected with hemopoietic stem cells (HSCs) along with donor BM stromal cells obtained after three to four weeks of culture. Histological examination revealed that hematopoietic colonies composed of both donor hemopoietic cells and stromal cells coexist in the liver of these mice. However, when donor HSCs plus BM stromal cells were administered i.v., neither the stimulatory effects on CFU-S formation nor the hemopoietic colonies in the recipient liver were observed. These findings suggest that the interaction of HSCs with stromal cells in the liver is the first crucial step for successful engraftment of allogeneic HSCs. It is likely that donor stromal cells and HSCs trapped in the liver migrate into the recipient BM and spleen, where they form CFU-BM and CFU-S, respectively.

Receptor engagement on cells expressing a ligand for the tolerance-inducing molecule OX2 induces an immunoregulatory population that inhibits alloreactivity in vitro and in vivo

Increased survival of C57BL/6 renal allografts following portal vein donor-specific pretransplant immunization of C3H mice is associated with increased expression of the molecule OX2 seen on host dendritic cells, along with a marked polarization in cytokine production from lymphocytes harvested from the transplanted animals, with preferential production of IL-4, IL-10, and TGF-beta on donor-specific restimulation in vitro, and decreased production of IL-2, IFN-gamma, and TNF-alpha compared with non-portal vein-immunized control transplanted mice. The increased renal allograft survival and the altered cytokine production are abolished by infusion of anti-mouse OX2 mAb (3B6). Infusion of a soluble OX2:Fc immunoadhesin can itself produce significant prolongation of xeno- and allografts in mice. We have used FITC-conjugated OX2:Fc to characterize cells expressing a ligand (OX2L) for OX2, and provide evidence that subpopulations of LPS-stimulated splenic macrophages, Con A-activated splenic T cells, and the majority (>80%) of gammadeltaTCR(+) T cells express this ligand. We show below that F4/80(+), OX2L(+) splenic macrophages, admixed with OX2:Fc, represent a potent immunosuppressive population capable of causing more profound inhibition of alloreactivity in vitro or in vivo than that seen using either OX2:Fc or OX2(+) (or OX2L(+)) cells alone. Immunoregulation by this OX2L(+) population occurs in an MHC-restricted fashion.

Evidence for persistent expression of OX2 as a necessary component of prolonged renal allograft survival following portal vein immunization

Following portal vein (pv) pretransplant immunization of C3H mice, there is an early (within 2 days) increase in expression of the molecule OX2 seen on host dendritic cells (DC), along with increased survival of C57BL/6 renal allografts transplanted within 24 h of pv immunization. In addition, there is a marked polarization in cytokine production from lymphocytes harvested from the transplanted animals, with preferential production of IL-4, IL-10, and TGFbeta on donor-specific restimulation in vitro, and decreased production of IL-2, IFN-gamma, and TNFalpha compared with non-pv-immunized control transplanted mice. Both the increased renal allograft survival and the altered cytokine production are abolished by infusion of anti-mouse OX2 monoclonal antibody (3B6), even when antibody infusion is begun as late as 10 days following transplantation. Quantitative PCR analysis independently shows that OX2 expression is increased in the spleen and liver of transplanted mice as late as 21 days following pv immunization. In vitro studies with an OX2:Fc immunoadhesion had suggested that immunosuppression induced by this soluble form of the OX2 molecule was dependent primarily upon an early (OX2-dependent) signal. This discrepancy between in vivo and in vitro data possibly reflects a role for OX2 in the in vivo recruitment of other (immunregulatory) cells. Consistent with this hypothesis, regardless of the time (posttransplantation) of in vivo infusion of anti-OX2 antibody, within 2 days we observed a decline in the functional activity of a previously characterized immunoregulatory gammadeltaTCR(+) cell population, which can be monitored by its ability to regulate cytokine production in vitro.

Regulation of gene expression of murine MD-1 regulates subsequent T cell activation and cytokine production

The immunoadhesin (OX2:Fc) comprising the extracellular domain of murine OX2 linked to IgG2aFc, inhibits production of IL-2 and IFN-gamma by activated T cells and increases allograft and xenograft survival in vivo. Increased expression of OX2 on dendritic cells (DC) in vivo following preimmunization via the portal vein is also associated with elevated expression of MD-1. We have used antisense oligodeoxynucleotides (ODNs) to MD-1 to investigate the effect of inhibition of expression of MD-1 by DC on their function as allostimulatory cells. We also investigated by FACS analysis the cell surface expression of OX2, CD80, and CD86 on DC incubated with ODN-1 blocking MD-1 expression. Blocking MD-1 gene expression inhibits surface expression of CD80 and CD86, but not of OX2. DC incubated with ODN-1 to MD-1 did not stimulate IL-2 or IFN-gamma production, but generated cells able to suppress, in a second culture of fresh DC plus allogeneic T cells, production of IL-2 and IFN-gamma. This inhibition was blocked by anti-OX2 mAb. Infusion of DC preincubated with ODN-1 prolonged renal allograft survival, an effect also reversed by anti-OX2 mAb. By FACS, incubation of DC with anti-MD-1 Ab to promote capping eliminated cell surface expression of MD-1 and CD14 without altering DEC205, DC26, CD80, CD86, or OX2 expression. Thus OX2 and MD-1 are independent surface molecules on DC that may reciprocally regulate T cell stimulation. MD-1 is linked to CD14, a "danger receptor complex," and activation of this complex can regulate cell surface expression of CD80/CD86, which signal T cells.

Fetal microchimerisms in the mother: immunologic implications

The previously held concept that the fetus is completely separated from the mother, especially by trophoblasts that line the outer layer of the placenta, has recently been questioned. It has recently been shown that fetal cells are detectable not only in the peripheral blood, but also in maternal skin and liver. Although the migration of fetal cells into the maternal circulation has been given a great deal of attention because of its implication in the prenatal diagnosis of genetic diseases, the potential role of such placental transfer of fetal cells in the pathogenesis of autoimmune diseases has only recently been considered. In patients with scleroderma, fetal cell-derived DNA was detected more frequently in the peripheral blood of patients than controls. This finding of a limited number of fetal cells in maternal tissues leading to microchimerism has been proposed to have a role in the induction of scleroderma. Although evidence for microchimerism has also been confirmed in a high frequency of liver tissues from patients with primary biliary cirrhosis (PBC), a similar high frequency was noted in control patients, which suggests that microchimerism by itself is unlikely to fully account for the pathogenesis of PBC. The finding of such a high frequency of fetal microchimerism in the liver suggests that this is a very common event, raising the possibility that the migration of fetal cells may be important in the induction and subsequent maintenance of tolerance against the fetus during pregnancy. In addition, it is clearly possible that such microchimerism could contribute to the pathogenesis of select autoimmune diseases.

Alterations in chemokine mRNA expression in animals receiving portal vein immunization and renal allo- or xenotransplantation precede altered cytokine production

We have analyzed chemokine mRNA expression in graft tissue of C3H/HEJ mice receiving allogeneic (C57BL/6) or xenogeneic [Lewis (LEW) rat donors] kidney grafts and correlated this with graft survival. Since donor-specific portal vein (pv) immunization is known to increase allo- and xenograft survival, in some cases recipients also received pretransplant pv or intravenous (iv) immunization; other animals received the antioxidant N-acetylcysteine (NAc) to examine the role of ischemia/reperfusion injury in the changes observed. Graft tissue and lymph nodes draining the respective grafts were obtained at various times posttransplantation and used for quantitative polymerase chain reaction analysis of mRNAs for different chemokines. In addition, lymphocytes were restimulated in culture with donor antigen and supernatants assayed for different cytokines. We observed that early increases in mRNA for MCP-1 preceded a polarization to type 2 cytokine production. Infusion of NAc twice daily for 4 days following transplantation further altered chemokine mRNA expression (increased MCP-1 and RANTES; decreased CINC); led to more enhanced type 2 cytokine production relative to control animals; and further increased xenograft survival. By use of heteroantibodies to different chemokines, anti-MCP-1 alone, but not antibodies to MIP-1alpha or RANTES, abolished this early polarization in cytokine production, implying a causal link between MCP-1 production and polarization in cytokine production. We conclude that manipulation of chemokine production early after transplantation might indirectly modify graft outcome by modifying cytokine production.

Persistent tolerance induced after portal venous injection of allogeneic cells plus cyclophosphamide treatment

The injection of allogeneic cells via the portal vein (p.v.) is known to reduce responses to donor-alloantigens. In the present study, we have obtained persistent tolerance across Mls and multiple minor histocompatibility complexes by p.v. preimmunization followed by the administration of cyclophosphamide (CY). A hundred percent survival of (BALB/c x DBA/2)F1 (CDF1) skin grafts for more than 200 days was observed when BALB/c mice were preimmunized with spleen cells of CDF1 (3 x 10(7)) via the p.v. and administered 300 mg/Kg CY 2 days after the p.v. injection. Comparable survival of the skin graft was observed when bone marrow cells instead of spleen cells were p.v. preimmunized. However, the survival rate was significantly decreased when LPS-stimulated blastic cells were p.v. preimmunized. Microchimerism has been observed in the liver, thymus, bone marrow and peripheral blood of recipients. V beta 6+ cells decreased in CD4+ cells of recipients of the p.v. preimmunization plus CY treatment. However, there was no difference in the decrease in V beta 6+ cells between recipients accepting the CDF1 skin grafts and recipients that had rejected the skin grafts. Furthermore, no intrathymic depletion of the V beta 6+ cells was observed. From these results, it is suggested that, rather than clonal deletion, other mechanisms such as clonal anergy or suppression may be involved in the induction of persistent tolerance after the p.v. preimmunization plus CY treatment.

A role for persisting antigen, antigen presentation, and ICAM-1 in increased renal graft survival after oral or portal vein donor-specific immunization

BACKGROUND

We studied the mechanism behind increased renal allotransplant survival when C3H mice received donor-specific portal vein or oral immunization with C57BL/6 cells. Both regimens lead to donor-specific increased graft survival, in association with decreased production of cytotoxic T lymphocytes and altered cytokine production from host lymphocytes (decreased interleukin [IL]-2 production; increased IL-4, IL-10, and transforming growth factor-beta).

METHODS

We examined a role for persistent donor-derived antigen, in association with host dendritic cells, as well as a role for intercellular adhesion molecule-1 (ICAM-1), in the maintenance of unresponsiveness in host C3H spleen cells to donor antigen. We investigated whether there was a cooperative interaction between donor dendritic cells (DC) and host hepatic mononuclear cells in the induction of immunoregulation in C3H cells.

RESULTS

In mice with surviving renal grafts, donor antigen, in association with host DC, induced the recall of cytotoxicity from C57BL/6 immune C3H spleen cells and IL-4 but not IL-2 production, despite the decreased cytotoxicity seen in the renal transplant recipients themselves. Fresh donor DC induced IL-2 but not IL-4 production. Blocking expression of ICAM-1 on donor grafts, either with anti-ICAM-1 monoclonal antibodies after renal grafting or using grafts from ICAM-1 "knockout" mice, led to further increased survival. Cultured C3H responder spleen cells, incubated with C57BL/6 DC and C3H hepatic cells, transferred hyporesponsiveness to C57BL/6 cells in vitro and in vivo (as assayed by survival of C57BL/6 renal allografts).

CONCLUSIONS

Our data suggest a role for ICAM-1, persistent donor antigen (on host DC), and accessory hepatic monocytes in the induction and maintenance of tolerance after portal vein immunization.

Increased expression of the novel molecule OX-2 is involved in prolongation of murine renal allograft survival

BACKGROUND

Portal venous (p.v.) peritransplant immunization with dendritic cells from bone marrow cultures, along with cyclosporine (10 mg/kg), produces antigen-specific increased renal allograft survival compared with recipients receiving intravenous (i.v.) immunization. Increased survival is associated with altered cytokine production from recipient T cells restimulated with donor antigen. We used a suppressive subtractive hybridization approach to explore a role in the regulation of transplant rejection for other genes differentially expressed after p.v. immunization.

METHODS

Subtractive hybridization was performed using tissue from p.v. and i.v. immunized mice and a novel polymerase chain reaction-based approach. A gene-bank search was used to identify the source of the differentially expressed cDNAs. One product, the mouse homologue of rat OX-2, was further analyzed using Western gels and FACS analysis of dendritic cells (NLDC145+) isolated from p.v.-immunized mice.

RESULTS

Eighty cDNA clones were obtained by suppressive subtractive hybridization. Differential expression was confirmed in Northern RNA blots. One clone showed sequence homology to a gene encoding a molecule on rat dendritic cells (MRC OX-2), with homology to genes encoding the costimulatory molecules CD80 (B7-1) and CD86 (B7-2). In p.v.-immunized mice, a monoclonal antibody to the rat OX-2 molecule identified, by Western blot analysis, increased expression of a molecule with molecular weight (43 kDa) analogous to rat MRC-OX-2; labels (by FACS analysis) indentified increased numbers of a population of cells staining with NLDC145; and blocks indentified increased graft survival.

CONCLUSION

Our data suggest that OX-2 is functionally important in the increased graft survival seen in p.v.-immunized mice receiving renal allografts.

Analysis of cytokine production and V beta T-cell receptor subsets in irradiated recipients receiving portal or peripheral venous reconstitution with allogeneic bone marrow cells, with or without additional anti-cytokine monoclonal antibodies

Irradiated (800 rads) AKR mice received intravenous (i.v.) reconstitution with a mixture of B10.BR T-depleted bone marrow cells and spleen cells. Only in groups of mice treated additionally with i.v. cyclophosphamide (Cy; 150 mg/kg), 24 hr before transplantation, was long-term (> 60% at 50 days) survival seen. In mice receiving only irradiation all animals died by 30 days post-transplantation. Histological changes consistent with graft-versus-host disease (GVHD) were seen in the liver of reconstituted mice at 30 days, along with an organ-specific increase in V beta 3 T-cell receptor-positive (TCR+) cells. No such increase in V beta 3 TCR+ cells was seen in the spleen from the same mice. These data are consistent with a tissue antigen-driven expansion of V beta 3 TCR+ cells associated with GVHD in the liver in this model. When we analysed cytokine production in vitro from CD3+ cells restimulated with 'host' (AKR) antigen-presenting cells (APC), we found a transition in cytokine production from preferential synthesis of type-1 cytokines [interleukin-2 (IL-2) and interferon-gamma (IFN-gamma)] at early times (day 15) post-reconstitution to increased production of type-2 cytokines [IL-4, transforming growth factor-beta (TGF-beta) and IL-10] at later times (day 30) post-reconstitution in Cy-treated recipients. Animals not receiving Cy did not show this 'switch' in cytokine production at later time points. We have observed a similar polarization in cytokine production, along with increased graft survival, in recipients of vascularized and non-vascularized allografts after portal venous (p.v.), but not i.v., pretransplant donor-specific immunization. We next studied AKR mice receiving 800 rads and subsequently reconstituted with B10.BR stem cells via the p.v. route. Again these mice showed prolonged survival (> 50% at 50 days), with polarization to IL-4, IL-10 and TGF-beta on restimulation of CD3+ cells in vitro at 30 days post-transplant and increased V beta 3 TCR+ cells in the liver. Infusion of anti-IL-12 monoclonal antibodies into irradiated mice receiving i.v. cell reconstitution produced a similar pattern of changes to those seen after p.v. reconstitution, while a combination of anti-IL-10 and anti-TGF-beta monoclonal antibodies reversed the changes seen after p.v. reconstitution. These data are consistent with an important role for differential cytokine production in the regulation of GVHD following allogeneic bone marrow transplantation.

Induction of donor-specific T cell anergy by portal venous injection of allogeneic cells

The mechanisms behind tolerance induction by portal venous (pv) injection of allogeneic cells are investigated. When a hematopoietic stem cell (HSC)-enriched population of BALB/c bone marrow was pv injected into C57BL/6 mice, the response of the T cells in the B6 mice to BALB/c alloantigens in mixed lymphocyte reaction (MLR) decreased until day 4 after the injection. Neither clonal deletion of V beta 11+ T cell nor donor-specific suppressor activity was observed. When recipient T cells were separated into CD4+ and CD8+ cells, only the CD8+ cell population showed donor-specific tolerance. The donor cells were trapped and retained in the host liver. MHC class I antigens were highly expressed on the trapped cells whereas class II antigens or B7 costimulatory molecules were not. The tolerance to BALB/c alloantigens in MLR was obtained also by the pv injection of Meth A, a BALB/c-derived sarcoma cell line. However, tolerance was not induced by the pv injection of B7-transfected Meth A cells. In addition to MLR, tolerance was also observed in DTH responses, and this was also due to the unresponsiveness of CD8+ cells to the donor alloantigens. However, the BALB/c-specific DTH responses were not suppressed after the pv injection of B7-transfected Meth A cells. These results strongly suggest that the tolerance induced by pv injection of allogeneic cells is due to clonal anergy generated by the absence of costimulatory signals in the interaction between donor-specific CD8+ T cells and donor hematopoietic cells trapped in the host liver.

The effect of immunomodulation of stimulator antigen presenting cells on subsequent responder T-cell function

In this study, we examined whether lipopolysaccharide (LPS)-, interferon-gamma (IFN-gamma) or 16,16-dimethyl prostaglandin E2 (dmPGE2)-pretreatment of stimulator spleen cells from C57BL6 (B6) mice affects effector function of responder T-lymphocyte from C3H/HeJ mice. Stimulation of B6-derived splenic mononuclear cells (SMNCs) with LPS (10 micrograms/ml) prior to their utilization as stimulator cells in a mixed lymphocyte culture (MLC) resulted in an increase in responder T-lymphocyte proliferation compared to utilization of unstimulated SMNC (P < 0.05). IFN-gamma demonstrated similar effects in a dose dependent fashion with maximal stimulatory effect seen at 1000 U/ml. In contrast, pretreatment of stimulator SMNC with dmPGE2 resulted in dose-dependent inhibition of the responder T-lymphocyte proliferation with maximum inhibitory effect seen using a concentration of dmPGE2 of 10(-5) M. The presence of indomethacin in the MLC did not reverse this effect. These data demonstrate the effect of immunomodulation of stimulator spleen cells on subsequent T-lymphocyte function.

Graft-infiltrating cells in rats receiving orthotopic semiallogeneic small intestine transplantation with portal or systemic venous drainage

The effect of alterations in venous drainage, from either ivc to portal vein (pv), along with peritransplant systemic (ivc) or portal (pv) venous alloimmunization with irradiated semiallogenic cells, on cell subset recovery in lymphoid organs of Lewis rats receiving orthoptic small bowel allografts (from LewisXBrown Norway) F1, LBNF1) was examined. Combined portal, venous drainage and alloimmunization has been reported to increase graft/recipient survival in this model. FACS analysis using monoclonal antibodies specific for different lymphocyte subsets was performed on cell suspensions of peripheral (P) and mesenteric (M) lymph node (LN), small bowel intraepithelial lymphocytes (SBIEL), and Peyer's patch (PP) lymphocytes on days 2 and 8 posttransplantation. Donor cell contributions to these cellular analyses were estimated by comparison of FACS staining with polyclonal anti-Lewis or Lewis anti-LBNF1 antibodies. Control animals received syngeneic grafts. In both syngeneic and semi-allogenic transplants with pv or ivc drainage there was no consistent difference in cell subsets from in PLN compared with those of control nongrafted rats. Approximately 50% to 60% of these cells were alphabetaTcR+ with a CD4+/CD8+ ratio of 3-4:1 and a (CD4++CD8+)/alphabetaTcR+ ratio of 1:1. Some 5% to 12% ED3+ cells were also present. In IEL, MLN, and PP by contrast, there were significant differences in cells recovered from rats with ivc vs. pv drainage of grafts. The most striking changes reflected a decreased CD4+/CD8+ and alphabetaTcR+gammadeltaTcR+ cells in these tissues in rats predestined to show prolongation of allograft survival (ivc vs. pv injected IEL CD4/CD8+ ratios and alphabetaTcR+gammadeltaTcR+ ratios 1.0, 0.7 and 5.0, 1.0, respectively. These data are consistent with a proposed role for such gammadeltaTcR+ cells in the local regulation of graft rejection.

The role of ICAM-1 in the induction of antigen-specific T cell hyporesponsiveness

We have previously demonstrated that pre-transplant transfusion of allogeneic splenic mononuclear cells from B10.BR mice to C3H/HeJ recipient mice resulted in subsequent antigen specific skin graft prolongation and an associated predominance of IL-4-producing T lymphocytes. In this report, we examined the role of ICAM-1 in the induction of T cell hyporesponsiveness and skin graft prolongation following intrahepatic alloantigen delivery. C3H/HeJ mice receiving splenic cells from B10.BR mice intrahepatically showed antigen-specific enhanced skin graft survival. This graft survival was further prolonged following pre-treatment of infused cells with anti-ICAM-1. No such prolongation was seen following intravenous administration of cells in the presence or absence of anti-ICAM-1 pre-treatment. Anti-ICAM-1 infusion alone similarly had no effect when given intrahepatically or peripherally. T lymphocytes from the mice receiving intrahepatic splenic cells and anti-ICAM-1 produced significantly higher amounts of IL-4 compared to mice receiving intrahepatic cells alone or intravenous cells. PCR analysis of ICAM-1 mRNA transcripts demonstrated an increased expression of ICAM-1 in the spleen compared to the liver. These results suggest that ICAM-1 plays an important role in the induction of T cell hyporesponsiveness and allograft prolongation following the intrahepatic encounter of alloantigen.

Manipulation of xenogeneic skin and/or renal graft survival in the rat-mouse concordant combination by portal vein pretransplant transfusion

We have examined whether portal venous pretransplant transfusion, which has been shown to produce prolongation of rodent vascularized (small intestine, kidney) and nonvascularized (skin) allografts, in the absence of other nonspecific immunosuppression, can produce similar graft prolongation in animals receiving vascularized or nonvascularized xeno- (not allo-) grafts. Rat kidney or skin grafts were transplanted into mice after portal venous pretreatment with rat or mouse spleen cells. Animals in some groups received additional immunosuppressive regimens including drug therapy (methotrexate, cyclosporin A) or monoclonal antibody treatment (anti-CD4, anti-CD8). Animal survival and serum creatinine was followed daily, and lymphoproliferation, cytokine production (including cytokine mRNA in grafted mice) and anti-xenograft antibody production was measured at distinct time points postgrafting. Both portal venous pretransplant transfusion and anti-CD4 monoclonal antibody treatment led to increased graft survival. However, unlike the rodent allograft model, graft survival in these animals was not simply explained by altered Th1/Th2 ratios. Other mechanism(s), possibly including xenoantibody production, are likely of importance in the regulation of xenograft rejection.

Regulation of IFN-gamma and IL-10 synthesis in vivo, as well as continuous antigen exposure, is associated with tolerance to murine skin allografts

C3H/HEJ mice are rendered hyporesponsive to multiple minor incompatible (B10.BR) skin allografts by pretreatment with irradiated B10.BR lymphoid cells injected via the portal vein, but not the lateral tail vein. As assessed by PCR with lymphocytes taken from grafted mice, or by measuring cytokines in vitro from antigen-restimulated cells, this hyporesponsiveness is associated with decreased mRNA for IFN-gamma and IL-2 production, but enhanced mRNA for IL-4 and IL-10 production. In mice given B10.BR cells via the tail vein, but in addition injected every second day with anti-IFN-gamma antibody, similar enhanced graft survival (with diminished IFN-gamma/IL-2 and enhanced IL-4/IL-10 production) was seen. In a separate study spleen cells from pretreated mice were "parked" in lethally irradiated syngeneic mice for 21 days, along with B10.BR skin grafts to some of the recipients. Only when recipients received this reexposure to B10.BR antigen did adoptively transferred spleen cells show "persistence" of the ability to produce delayed graft rejection and preferential IL-4 production in vitro.

Migration patterns of lymphocytes following syngeneic heterotopic small bowel transplantation in rodents

Adult rats received syngeneic accessory small bowel grafts with venous drainage to either the portal vein (hetero-portal) or the inferior vena cava (hetero-systemic). Lymphoid cell recovery in different lymphoid organs (spleen, pooled peripheral lymph nodes, mesenteric nodes, Peyer's Patches) was evaluated at varying times (days 0-300) post-grafting. While minimal changes were observed for cell recovery in other organ tissues, lymphocyte recovery in Peyer's Patches of both host and graft small intestine of hetero-systemic animals was decreased from 10- to 100-fold with respect to hetero-portal recipients or non-operated controls. These changes were seen throughout the time course of the study. In additional experiments, lymphoid cells from different organs/donors were labelled in vitro with 111In and injected intravenously into normal/transplanted recipients. Recovery of 111In in various organs was assessed at 1 and 6 h postinjection. The major change seen was in the decreased ability of mononuclear cells derived from Peyer's Patches to migrate to small intestinal tissue (host and graft) in hetero-systemic recipients. In addition, Peyer's Patch cells from these animals 'homed' poorly to small intestine in non-operated animals by comparison with cells from normal rats (or hetero-portal donors).

Antigen presentation by murine splenic, but not hepatic, antigen-presenting cells to induce IL-2/IL-4 production from immune T cells is regulated by interactions between LFA-1/ICAM-1

Pretransplant transfusion of multiple minor histoincompatible spleen cells to naive recipient mice by the portal vein suppresses the ability of those animals to reject skin grafts from mice syngeneic with those used for transfusion, and decreases in vitro immunity on rechallenge with the same antigens, by comparison with mice receiving transfusion by the lateral tail vein. We have shown elsewhere that this is correlated with a diminished activation of Th1 cells for IL-2 production, without apparently affecting activation of Th2 cells for IL-4 production. Similar data are obtained by merely infusing hepatic (vs. splenic) antigen-presenting cells (APC) into normal mice, or by challenging immune cells in vitro with antigen-pulsed hepatic (vs. splenic) APC. However, when antigen-pulsed splenic APC are incubated with immune T cells in the presence of anti-LFA-1 monoclonal antibody (Mab), selective activation of Th2 cells (as is seen with hepatic APC) again occurs at the expense of activation of Th1 cells. Anti-LFA-1 Mab causes little perturbation in lymphokine production from T cells stimulated with hepatic APC. Using cDNA probes for IL-2 and IL-4 we show that T-cell activation in the presence of anti-LFA-1 Mab leads to selective inhibition of transcription of IL-2 mRNA.

Immunosuppression induced by hepatic portal venous immunization spares reactivity in IL-4 producing T lymphocytes

Immunization of naive or specifically primed C3H/HEJ with irradiated B10.BR spleen cells via the hepatic portal vein leads to an antigen specific decrease in the proliferative and cytotoxic response to B10.BR antigen assayed in vitro (and to increased graft survival of B10.BR grafts in vivo). This effect seems to be mediated in the main by a decrease in IL-2 production from CD4+ T lymphocytes of mice given antigen by the portal route, which is in turn caused by a decreased precursor frequency of IL-2-producing cells. No clear decrease in IL-4 production was seen. Hepatic APC isolated from mice receiving antigen via the portal vein were unable to induce IL-2 production from a C3H/HEJ anti-B10.BR cell line in vitro, in contrast to splenic APC derived from the same mice. Even when antigen was given by conventional (systemic) intravenous routes (in this case via the lateral tail vein) hepatic APC isolated from those mice were unable to stimulate IL-2 production from this cell line. Furthermore, 24 h exposure of a cell line to antigen pulsed hepatic APC left those cells refractory to a subsequent restimulation with antigen presented by splenic APC. Spleen lymphoid cells from primed mice challenged in vivo with B10.BR liver cells (i.v.) were similarly unable to produce IL-2 on rechallenge in vitro with irradiated B10.BR spleen cells, though no defect was seen if in vivo challenge was with B10.BR spleen cells. These data imply that presentation of multiple minor cell surface antigens by hepatic APC leads to specific anergization of IL-2 producing T cells, in a fashion which seems to be distinct from that previously reported as due to 'veto-like' activity.